1. Field of the Invention
The present invention relates to a method for forming a diffusion barrier layer, and more particularly to a method for forming a diffusion barrier layer for simultaneously forming a low resistance layer by way of a two-step quick heating treatment at low and high temperatures.
2. Description of the Prior Art
As semi-conductor devices have become finer and more highly integrated, a multilayer metal wiring process calls for a diffusion barrier layer between silicon and aluminum alloy in order to prevent spiking and the like caused by precipitation of aluminum used as conductivity membrane in a thin diffusion layer.
The diffusion barrier layer is formed by mixture of nitrogen with metals of high melting point such as Ti, W, Ta, Mo and the like.
However, when the diffusion barrier layer is directly vacuum-evaporated to the silicon, contact resistance goes up, thereby causing a low resistance layer to form between the diffusion barrier layer and the silicon, and reducing the contact resistance.
The low resistance layer is formed with silicide in metal of high melting point for forming the diffusion barrier layer.
FIGS. 1(A), 1B and 1(C) a re process drawings for illustrating a forming method of diffusion barrier layer according to the prior art.
As illustrated in FIG. 1(A), a silicon substrate (11) formed with impurity diffusion region(B) is formed with an insulation membrane (15).
An opening (17) is formed at a predetermined area of the insulation membrane (15) by way of a conventional photolithographic method, thereby exposing the diffusion region (13).
As illustrated in FIG. 1(B), an overall surface of the aforementioned structure is vacuum-evaporated by metals of high melting points such as Ti, W, Ta, Mo and the like in thickness of 50.about.200 .ANG. by way of sputtering method or chemical vapor deposition (CVD) method.
Successively, the surface is vacuum-evaporated by the metals of high melting points such as Ti, W, Ta, Mo and the like in thickness of 300.about.500 .ANG. under nitric atmosphere by way of sputtering or CVD method.
The vacuum-evaporated layer is quickly heat-treated at a high temperature of 700.about.1,000 degrees celsius under the nitric or ammoniac atmosphere.
At this point, a unit high melting point metal layer formed at an upper area of the diffusion region (13) reacts with the silicon substrate, silicifies and becomes a low resistance layer (19), and the metal layer of high melting point containing the nitrogen is nitrified to become a diffusion barrier layer (21).
As illustrated in FIG. 1, the diffusion barrier layer (21) is vacuum-evaporated at an upper area thereof with aluminum or the like to thereby form a conductivity layer (43).
Then, the conductivity layer (43), diffusion barrier layer (21) and low resistance layer (19) are removed by way of photolithographic method which are vacuum-evaporated at the predetermined upper area of the isolation membrane (15) other than the opening (17).
In the aforementioned description, heat change reaction during the quick heating treatment occurs quite differently according to a processed temperature, and respective thickness of generated diffusion prevention layer and low resistance layer is determined accordingly as the reactions are all stopped the moment the two layers collide.
At this point, the metal having a high melting point reacts rapidly with the silicon and nitrogen, by which the diffusion prevention layer and the low resistance layer are thickly formed as well.
However, there is a problem in that, when the low resistance layer is thickly formed, the diffusion prevention layer becomes thin, thereby failing to form a thickness that is sufficient for prevention of diffusion.
There is another problem in that the silicon substrate and the low resistance layer become uneven at intersurfaces thereof, and stress is generated due to volume change of the low resistance layer thereby resulting in junction leakage.